The control mechanisms of IgE production are under study utilizing a mouse model system. Attempts are being made to purify murine IgE and develop a radio-immunoassay capable of quantitating the small amounts of IgE present in mouse serum (estimated to be less than 1.0 micron/ml): for this purpose an IgE-hydriodoma has been produced. Mice exposed to nebulized antigens are incapable of an IgE response when later immunized with the same antigen. The mechanism of this phenomenon is under investigation.